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  • Whats wrong with the following code, its not compiling

    - by Ganesh Kundapur
    #include <iostream> #include <vector> using namespace std; class Base { public: void Display( void ) { cout<<"Base display"<<endl; } int Display( int a ) { cout<<"Base int display"<<endl; return 0; } }; class Derived : public Base { public: void Display( void ) { cout<<"Derived display"<<endl; } }; void main() { Derived obj; obj.Display(); obj.Display( 10 ); } $test1.cpp: In function ‘int main()’: test1.cpp:35: error: no matching function for call to ‘Derived::Display(int)’ test1.cpp:24: note: candidates are: void Derived::Display() On commenting obj.Display(10), it works.

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  • The C vs. C++ way

    - by amc
    Hi, So I have to write a program that will iterate through an image and record the pixel locations corresponding to each color pixel that appears in it. For example, given http://www.socuteurl.com/fishywishykissy I need to find the coordinates of all yellow, purple, dark pink, etc pixels. In C++ I would use a hash table to do this. I would iterate through the image, check each pixel's value, look up that value and either add to a vector of pixel coordinates if it were found or add a new entry to the table if the value were not already there. The problem is that I may need to write this program in pure C instead of C++. How would I go about doing this in C? I feel like implementing a hash table would be pretty obnoxious and error-prone: should I avoid doing that? I'm pretty inexperienced with C and have a fair amount of C++ experience, if that matters. Thanks.

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  • R: Cut and labels/breaks length conflict

    - by AkselO
    I am working with the cut function to prep data for a barplot histogram but keep running into a seeming inconsistency between my labels and breaks: Error in cut.default(sample(1:1e+05, 500, T), breaks = sq, labels = sprintf("$%.0f", : labels/breaks length conflict Here is an example. I pretend that it is income data, using a sequence of 0 to $100,000 in bins of $10,000. I use the same variable to generate both breaks and labels, with minor formating on the label side. I thought they might for some reason have different lengths when comparing to a character vector, but they appear to have the same length, still. > sq<-seq(0,100000,10000) > cut(sample(1:100000, 500, T),breaks=sq,labels=sprintf("$%.0f",sq)) > length(sprintf("$%.0f",sq)) [1] [11] > length(sq) [1] [11]

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  • Autocomplete for generic types in Eclipse

    - by AvrDragon
    "Refer to objects by their interfaces" is a good practise, as mentioned in Effective Java. So for example i prefer List<String> al = new ArrayList<String>(); over ArrayList<String> al = new ArrayList<String>(); in my code. One annoying thing is that if i type ArrayList<String> al = new and then hit Ctrl+Space in Eclipse i get ArrayList<String>() as propostal. But if i type List al = new and then hit Ctrl+Space i will get only propostal to define anonymous inner class, but not propostals such as new ArrayList<String>(), what is 99% the case, or for example new Vector<String>(). Is there any way to get the subclasses as propostals for generic types?

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  • Calculating the null space of a matrix

    - by Ainsworth
    I'm attempting to solve a set of equations of the form Ax = 0. A is known 6x6 matrix and I've written the below code using SVD to get the vector x which works to a certain extent. The answer is approximately correct but not good enough to be useful to me, how can I improve the precision of the calculation? Lowering eps below 1.e-4 causes the function to fail. from numpy.linalg import * from numpy import * A = matrix([[0.624010149127497 ,0.020915658603923 ,0.838082638087629 ,62.0778180312547 ,-0.336 ,0], [0.669649399820597 ,0.344105317421833 ,0.0543868015800246 ,49.0194290212841 ,-0.267 ,0], [0.473153758252885 ,0.366893577716959 ,0.924972565581684 ,186.071352614705 ,-1 ,0], [0.0759305208803158 ,0.356365401030535 ,0.126682113674883 ,175.292109352674 ,0 ,-5.201], [0.91160934274653 ,0.32447818779582 ,0.741382053883291 ,0.11536775372698 ,0 ,-0.034], [0.480860406786873 ,0.903499596111067 ,0.542581424762866 ,32.782593418975 ,0 ,-1]]) def null(A, eps=1e-3): u,s,vh = svd(A,full_matrices=1,compute_uv=1) null_space = compress(s <= eps, vh, axis=0) return null_space.T NS = null(A) print "Null space equals ",NS,"\n" print dot(A,NS)

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  • Why am I not getting correct result when I calculate exponent with ^ in C++?

    - by xbonez
    I am using Bode's formuala to calculate distance of nth planet from sun dist = (4 + 3*(2^(n-2)))/10 If I calculate the distance this way, I get the right values: dist[2] = ((4 + 3*1)/10.0) ; dist[3] = ((4 + 3*2)/10.0) ; dist[4] = ((4 + 3*4)/10.0) ; But doing it this way, gives me incorrect values: vector <double> dist(5); for (unsigned int i = 2; i < 5; i++) { dist[i] = ((4 + 3*(2^(3-2)))/10.0) ; } Why so?

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  • measuring uncertainty in matlabs svmclassify

    - by Mark
    I'm doing contextual object recognition and I need a prior for my observations. e.g. this space was labeled "dog", what's the probability that it was labeled correctly? Do you know if matlabs svmclassify has an argument to return this level of certainty with it's classification? If not, matlabs svm has the following structures in it: SVM = SupportVectors: [11x124 single] Alpha: [11x1 double] Bias: 0.0915 KernelFunction: @linear_kernel KernelFunctionArgs: {} GroupNames: {11x1 cell} SupportVectorIndices: [11x1 double] ScaleData: [1x1 struct] FigureHandles: [] Can you think of any ways to compute a good measure of uncertainty from these? (Which support vector to use?) Papers/articles explaining uncertainty in SVMs welcome. More in depth explanations of matlabs SVM are also welcome. If you can't do it this way, can you think of any other libraries with SVMs that have this measure of uncertainty?

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  • struct with template variables in c++

    - by monkeyking
    I'm playing around with template, so I'm not trying to reinvent the std::vector, I'm trying to get a grasp of templateting in c++. Can I do the following template <typename T> typedef struct{ size_t x; T *ary; }array; What I'm trying to do is a basic templated version of typedef struct{ size_t x; int *ary; }iArray; It looks like its working if I use a class instead of struct, so is it not possible with typedef structs? thanks

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  • What is a good standard for code width?

    - by BillyONeal
    Hello everyone :) I've heard in several places that it's bad to have code that is too wide onscreen. For example: for (std::vector<EnumServiceInformation>::const_iterator currentService = services.begin(); currentService != services.end(); currentService++) However, I've heard many arguments for 80 character wide limits. I'm assuming this 80 character limit comes from the traditional command prompt, which is typically 80 characters wide. However -- most of us are working on something much better than a typical command prompt, and I feel that using an 80 character limit encourages use of variable names that are far too short and do not describe what the variable is used for. What is a reasonable limit for a new project with no existing coding width standard?

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  • Collection type generated by for with yield

    - by Jesper
    When I evaluate a for in Scala, I get an immutable IndexedSeq (a collection with array-like performance characteristics, such as efficient random access): scala> val s = for (i <- 0 to 9) yield math.random + i s: scala.collection.immutable.IndexedSeq[Double] = Vector(0.6127056766832756, 1.7137598183155291, ... Does a for with a yield always return an IndexedSeq, or can it also return some other type of collection class (a LinearSeq, for example)? If it can also return something else, then what determines the return type, and how can I influence it? I'm using Scala 2.8.0.RC3.

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  • Determining if two rays intersect

    - by Faken
    I have two rays on a 2D plane that extend to infinity but both have a starting point. They are both described by a starting point and a vector in the direction of the ray extending to infinity. I want to find out if the two rays intersect but i don't need to know where they intersect (its part of a collision detection algorithm). Everything i have looked at so far describes finding the intersection point of two lines or line segments. Anyone know a fast algorithm to solve this?

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  • Unexpected result from reduce function

    - by StackedCrooked
    I would like to get the smallest element from a vector. For this I use combine the reduce and min functions. However, when providing my own implementation of min I get unexpected results: user=> (reduce (fn [x y] (< x y) x y) [1 2 3 2 1 0 1 2]) 2 user=> (reduce min [1 2 3 2 1 0 1 2 3]) 0 The reduce with standard min returns 0 as expected. However, when I provide my own implementation it returns 2. What am I doing wrong?

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  • [MATH]Project an axis to a plane

    - by Robert
    how do i project the X axis to a plane if the plane is defined by three points? see pic here: http://129.25.16.135:2080/v6.5/books/usb/graphics/iconventions-local-surfaces.png The default local 1-direction is the projection of the global x-axis onto the surface. If the global x-axis is within 0.1° of being normal to the surface, the local 1-direction is the projection of the global z-axis onto the surface. let's suppose that these points are: t1 = [-0.362879991531372, 0.357021987438202, -0.373737007379532] t2 = [-0.383525013923645, 0.371621012687683, -0.383549988269806] t3 = [-0.383534014225006, 0.34629300236702, -0.38544899225235] is the vector [0.78280971952246, -0.0307519963686645, 0.411184845614438] correct answer in this case? i've calculated the angle between the surf and x (1,0,0) is ~28°. and can you give the entire procedure for the calculation, because i'm just puzzled.

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  • Some exam questions about C++ vectors and arrays...

    - by xbonez
    Hey guys, I have a CS exam tomorrow. Just want to get a few questions cleared up. Thanks a lot, and I really appreciate the help. Que 1. What are parallel vectors? Vectors of the same length that contain data that is meant to be processed together Vectors that are all of the same data type Vectors that are of the same length Any vector of data type parallel Que 2. Arrays are faster and more efficient than vectors. True False Que 3. Arrays can be a return type of a function call. True False Que 4. Vectors can be a return type of a function call. True False

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  • allocator with no template

    - by Merni
    Every stl container take an allocator as a second object, template < class T, class Allocator = allocator<T> > class vector; If you write your own class It is possible to use your own allocator. But is it possible to write your own allocator without using templates? For example, writing this function is not easy if you are not allowed to use templates pointer allocate(size_type n, const_pointer = 0) { void* p = std::malloc(n * sizeof(T)); if (!p) throw std::bad_alloc(); return static_cast<pointer>(p); } Because how could you know the size of T?

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  • Why can I derived from a templated/generic class based on that type in C# / C++

    - by stusmith
    Title probably doesn't make a lot of sense, so I'll start with some code: class Foo : public std::vector<Foo> { }; ... Foo f; f.push_back( Foo() ); Why is this allowed by the compiler? My brain is melting at this stage, so can anyone explain whether there are any reasons you would want to do this? Unfortunately I've just seen a similar pattern in some production C# code and wondered why anyone would use this pattern.

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  • C++ Array of Variable sized Arrays

    - by adam
    I am very new to C++ and I realise the following is not necessarily as easy as I'd like it to be, but I'd really appreciate a more expert opinion. I am essentially trying to achieve a dynamic iteration over a variable sized array of variable sized arrays similar to the following. String *2d_array[][] = {{"A1","A2"},{"B1","B2","B3"},{"C1"}}; for (int i=0; i<2d_array.length; i++) { for (int j=0; j<2d_array[i].length; j++) { print(2d_array[i][j]); } } Is there a reasonable way to do this? Perhaps by using a vector, or another struct? Thanks :)

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  • HELP!! Implementing a search to match the specified author and displaying a book by the specified publisher

    - by Brian
    Hey guys! So i'm having problems with my assignment. I successfully got it to run multiple last names by the author, but now, I need to find all books by author, which means searching the collection for all books that match the specified author and I also need to find all books by publisher, which displays a list of books by the specified publisher. How would I implement this? Would I use string or vector? Any help will be much appreciated!

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  • Designing entire webpages as SVG files

    - by user1311390
    Disclaimer I realize that given the absurdity of the title, this sounds like a troll. However, it's a genuine question. My background involves OpenGL / x86 assembly. I've recently started learning web programming. I really like SVG + CSS, and was wondering -- why do people not design entire webpages in SVG? Context SVG provides beautiful primitive: quadratic + cubic bezier curves; lines + filling -- all as vector graphics SVG provides text SVG provides affine transformations Questions Are there examples of people designing entire websites as a giant SVG file? If not, what the limitations? Are there performance hits when using SVG primitives as opposed to divs/tables?

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  • Conflicts with file from package mysql-5.0.77

    - by Whiteyq
    I'm trying to install APC (Alternative PHP Cache) on a CentOs dedicated server. I've everything done apart from configuring phpize. Running :yum -y install php-devel gives me the following error file /usr/share/mysql/charsets/Index.xml from install of mysql-libs-5.1.57-1.el5.art.x86_64 conflicts with file from package mysql-5.0.77-4.el5_5.3.i386 etc etc for other languages So, i think the mysql version i have is too old & i more than likely need to upgrade mysql to version 5.1. Im reluctant to do this as a) its a live server (although only 3/4 domains) b) ive read ill read to recompile php if i upgrade To add to this i have plesk installed for managing domains & might need reinstalling/reconfiguring also. sorry for the long intro but its my first post & best to give as much info as possible, so my question is basically Is there any way i can run :yum -y install php-devel to get phpize working to complete installation of APC for the version of mysql i currently have installed? ie 5.0.77

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  • Javascript function returning number with two decimals...?

    - by muzzledBYbrass
    I have a function to return points along a line and my return comes back with two decimal points...? For example, a return of my variable px will be something like -88.4029.032940598. vx is the x vector and mult is the distance of the line plus distance to calculate the point. Here is the operation that is returning these values: var mult = parseFloat(mag + theUnit); var px = coord_one.x_point + (vx * mult); console.log(px); Never have seen this before- I appreciate any and all help!

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  • C++ typedef for partial templates

    - by Gokul
    Hi, i need to do a typedef like this. template< class A, class B, class C > class X { }; template< class B, class C > typedef X< std::vector<B>, B, C > Y; I just found that it is not supported in C++. Can someone advise me on how to achieve the same through alternative means? Thanks, Gokul.

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  • Filtering spectrum using FIR filters

    - by Alex Hoppus
    If i have signal values x[T] and filter coefficients b[i], i can perform filtering using convolution. Suppose i have spectrum of x (after FFT) and i need to perform filtering using filters coefficients, how can i perform this? I heard that in frequency domain it will be multiplying, rather than convolution (time domain). But i can't find an equation to use it. I have 614000 values in y = fft(x[T]) vector and 119 filter coefficients (generated using fdatool), i can't multiply them directly ... Thanks.

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  • IN r, how to combine the summary together

    - by alex
    say i have 5 summary for 5 sets of data. how can i get those number out or combine the summary in to 1 rather than 5 V1 V2 V3 V4 Min. : 670.2 Min. : 682.3 Min. : 690.7 Min. : 637.6 1st Qu.: 739.9 1st Qu.: 737.2 1st Qu.: 707.7 1st Qu.: 690.7 Median : 838.6 Median : 798.6 Median : 748.3 Median : 748.3 Mean : 886.7 Mean : 871.0 Mean : 869.6 Mean : 865.4 3rd Qu.:1076.8 3rd Qu.:1027.6 3rd Qu.:1070.0 3rd Qu.: 960.8 Max. :1107.8 Max. :1109.3 Max. :1131.3 Max. :1289.6 V5 Min. : 637.6 1st Qu.: 690.7 Median : 748.3 Mean : 924.3 3rd Qu.: 960.8 Max. :1584.3 how can i have 1 table looks like v1 v2 v3 v4 v5 Min. : 1st Qu.: Median : Mean : 3rd Qu.: Max. : or how to save those number as vector so i can use matrix to generate a table

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  • Can I use MFC objects in STL containers?

    - by Jesse Stimpson
    The following code doesn't compile for me in MSVC2005: std::vector<CMenu> vec(10); CMenu is an MFC menu object (such as a context menu). Through some testing I learned that CMenu does not have a public copy constructor. To do what I wanted to do, I needed to use a dynamic array. CMenu* menus = new CMenu[10]; // ... delete [] menus; Of course, now I've lost all the benefits of using an STL container. Do I have any other options?

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